1. Field of the Invention
The present invention relates to a printing apparatus having a feed mechanism for feeding paper to a printing portion including a printing head and a platen.
2. Description of the Related Art
Generally, a printing apparatus includes a print portion having a printing head and a platen confronting the print head. A paper supply roller is rotatably provided at an upstream side of the printing portion. Further, a paper feed roller is rotatably disposed in abutment with the paper supply roller. The paper feed roller and the paper supply roller cooperate to feed paper to the print portion.
According to a conventional printing apparatus, it becomes impossible to further feed the paper toward the print portion and to positively discharge the paper therefrom, once the tail end of the paper feed means at a downstream side of the print portion. Accordingly, the printing operation cannot be performed in a paper zone between the printing portion and the tail end of the paper. This problem is particularly recognized when printing on small sized paper such as a post card since the non-printed or blank portion occupies a relatively large area in comparison to the printed portion. Therefore, economical printing may not be attainable.
In order to overcome this drawback, Japanese Patent Publication No. 60-18549 discloses a supplemental roller at the downstream side of the print portion in addition to the rollers at the upstream side thereof. The supplemental roller is rotated at an angular speed equal to that of the upstream side roller, and has a diameter larger than that of the upstream roller. With the structure, the paper is fed by both upstream and downstream rollers under tension.
In this conventional printer, a pressure roller is provided in abutment with each of the upstream and downstream side rollers to apply tension to the paper undergoing feeding. Even though the pressure roller may be movable toward and away from the supplemental roller by manual operation, the pressure roller is always in contact with the supplemental roller during the printing operation. Therefore, if there are dimensional errors with respect to at least one of the upstream and downstream side rollers, excessive tension may be applied to the paper, or excessive slacking may occur during printing operation.
Further, due to the difference in diameters between these rollers for tension application to the paper, it becomes impossible to feed paper in the reverse direction. During reverse feeding, paper slacking occurs at the print portion due to the diametrical difference between the rollers, and due to the fact that both the upstream and downstream sides of the paper with respect to the print portion are subjected to nipping.